Come on my friend, that is he most regressive tax feasible. How much of his income does Bill Gates spend on buying "taxable items"? How much does a middle income family? You'll transfer the load of taxes to those that can least afford it. If I or Bill Gates buy stock or other properties, will you tax each buying transaction? You'll say no (since if you say yes, you killed the equities market". So where does it applies? Real estate, bonds, collectible, art? If a company buys a thousand tons of steel, do they pay 15% on it? Does it apply only to retail, maybe all intermediary buying and selling should be taxed as well. If not, how do you differentiate? You just create another quagmire bureaucracy to administer that one.
Zeev